Introduction
Let me begin this presentation by stating that biological agents (natural enemies) have been operating in their natural habitats to control pest populations since time immemorial. However, the natural enemies are sometimes absent or in limited population necessitating the need for human reared natural enemies to augment their population. As outlined in Hajek (p. 62), augmentation thus refers to the release of large numbers of human-reared natural enemies to control the population of certain pests. It utilizes domestic natural enemies and rests on the hypothesis that the natural enemies are domestically available, but their population needs to be augmented. With that brief introduction let me present two strategies for augmentation.
Inundative Biological Control
This strategy is used for short-term rapid control of pests. It involves the release of large amounts of commercially reared natural enemies to lessen the population of a damaging or potentially damaging pest (Hajek p. 62). However, I need to clarify that the control is only due to the natural enemy and not the progeny as no reproduction of the natural enemy is expected. It is expected that the released agents would attack and kill sufficiently high amounts of the pest, but should there be an increase in the population of the pest after the first release, then release can be repeated to ensure success (p. 63). It is important to note that the release can also be repeated in cases whereby the crop is long-lived and is thus susceptible to future attacks by the pest. Inundative strategy is often considered expensive since it requires the release of large amounts of commercially reared species hence only recommended in certain situations. Practical examples of inundative pest control include the use of Trichogramma to control the population of moths as well as the use of microbial insecticides, especially those containing Bacillus thuringiensis.
Inoculative Biological Control
What about inoculative biological control? In this strategy, the natural enemy is released in bits throughout the pest period. The release starts when the pest’s population is still negligible (Hajek p. 64). Unlike in the case of inundative strategy, the natural enemies released are expected to reproduce hence the control is due to both the natural enemy initially released and its progeny (p. 64). Also, note that inoculative biological control aims at long-term control of the pest by establishing itself and ensuring that the population of the pest is kept below the economic injury level. Examples of inoculative biological control include the use of predatory mites for pest control in greenhouses and the use of Bacillus papillae (inoculated in soils) to control Japanese beetle grubs.
Inundative Vs Inoculative Biological Pest Control
I have summarized the differences between these two strategies as follows:
Production of Natural Enemies by Industry
The Need for a Market
I would like to state that there exists a surprisingly low demand for natural enemies among growers, which hampers the industry’s efforts to invest in the development of new augmentative products. According to van Lenteren (p. 14), Europe accounted for more than half of the global demand while Africa recorded the least demand in 2008. Most growers also prefer established species to new species. By the year 2000, 130 species were available for release, but only 30 species constituted 90% of sales (Hajek p. 78). Another challenge to the mass production of augmentative products is the unpredictable need for pest control, which might render products useless since they do not have a long storage lifespan hence losses to producers (Hajek p. 68).
Host Specificity of the natural enemy
The Natural enemies with a limited host range are considered environmentally friendly, but may not attract high sales among growers who would prefer natural enemies with a wider host range (Hajek p. 68). The low sales potential for host-specific tiny, but visible organisms’ natural enemies thus does not justify their mass production.
Products for Use
Macro organisms
Macro organisms include very such as arthropod parasitoids and predators, and insect parasitic nematodes (Hajek p. 69-70). They are host and climate-specific meaning their success depends on the prevailing climatic condition. These products also have a short storage lifespan. However, research on genetic manipulation of available natural enemy species is underway in a bid to expand their host range as well as reduce their environmental sensitivity (p. 70). Mass production of macro-organisms is done in insectaries where large colonies of their hosts are also reared. There is a need for quality assurance during production, storage and release. Field release can be done manually by hand or use of helicopters in case of forest application.
Microorganisms
Microorganisms include microscopic organisms such as pathogens including viruses, bacteria and fungi. They can be produced in the laboratory. While bacterial pathogens only require a simple media for their production, viruses require a living host for their production. They also require quality assurance during production, storage transport and release. Microorganisms can be released using existing pesticide application equipment.
Regulation
While there is a laxity in the regulation of macro-organisms, the production and use of microorganisms in countries such as the U.S and Europe are strictly regulated. The introduction of new microbial pesticides and fungicides requires a three-tier test to guarantee their ecological safety (Hajek p. 77). In the U.S., field test of pathogens in less than ten acres piece of cropland for one year would not require any registration, but if the pathogen is to be tested on more than ten acres of cropland, then Experimental Use Permit from EPA is mandatory. Both microorganisms have to be registered by EPA under Federal Insecticide Fungicide and Rodenticide Act (FIFRA- 1972) (3 SCH, sec. a).
Natural Enemies Commercially Available for Release
Information on available products for the augmentative release can be obtained from reviews, directories or pest control-related websites such as the Association of Natural Bio-control Producers. Even though some products are only available for use in specific countries due to strict regulations on transport, the number of species available for commercial use has been increasing over the years as illustrated in slide 9. Macro-organisms are often available for use only in greenhouses, but a few such as predatory mites and arthropods such as beetles and caterpillars are available for field release (Hajek p. 77). Micro-organisms are often available in the form of bacteria, fungi and virus-based bio-pesticides available for augmentative field release.
The video: Bio Works supplies predatory mites to Ricardoes
My research for this presentation led me to this video, which I consider informative in this topic. The video is a one minute, 25 seconds case study illustration of predatory mites in action in a tomato and strawberry greenhouse farm in Port Maquarie, Australia.
Works Cited
Federal Insecticide Fungicide and Rodenticide Act (FIFRA), 3 SCH, sec. a (1972). Print. Hajek, Anne. Natural Enemies: An Introduction to Biological Control. Cambridge: Cambridge University Press, 2004. Google Books. Web.
van Lenteren, Joop. “The State of Commercial Augmentative Biological Control: Plenty of Natural Enemies, but a Frustrating Lack of Uptake”. BioControl 57 (2012): 1- 20. Print.